Bone tendon bone assembly

ABSTRACT

The invention is directed toward a bone block, a bone-tendon-bone assembly and method of tendon reconstruction in which at least one tendon replacement is extended between two bone blocks and fixed within each of two bone tunnels in the bones of a joint using interference screws. Each bone block has a central through going bore and at least one substantially parallel channel longitudinally cut in the exterior of the bone block body in which the ligament replacements are seated. One end of each bone block has a rounded recess leading from the central bore to the exterior parallel channel.

RELATED APPLICATION

There are no related applications.

FIELD OF INVENTION

The present invention is generally directed toward a surgical implantproduct and more specifically is a shaped allograft bone-tendon-boneimplant assembly.

BACKGROUND OF THE INVENTION

Failed ligaments, such as the anterior or posterior cruciate ligamentsin the knee joint, significantly limit physical activity and potentiallycause chronic knee problems. The anterior cruciate ligament (hereinafterACL) and the posterior cruciate ligament (PCL) to a lesser extent areoften torn during sports related injuries or as result of traumaticstresses. Ligament reconstruction with allograft and autograft tissuehas been shown to improve joint function and provide long termimprovement in restoration of physical activity. A common surgicalmethod of repair of an ACL is harvesting a patients patellar tendon withbone blocks from the tibia and patella. The bone-patellar tendon-boneimplant offers several advantages, including the high initial tensilestrength, stiffness, proper length, rigid fixation and directbone-to-bone incorporation.

The anterior cruciate ligament of the knee functions to resist anteriordisplacement of the tibia from the femur at all flexion positions. TheACL also resists hyper-extension and contributes to rotational stabilityof the fully extended knee during internal and external tibial rotation.The ACL may also play a role in proprioception. Structurally, the ACLattaches to a depression in the front of the intercondylar eminence ofthe tibia extending postero-superiorly to the medial wall of the lateralfemoral condyle.

Partial or complete tears of the ACL are very common, comprising about100,000 outpatient procedures in the U.S. each year. The preferredtreatment of the torn ACL is ligament reconstruction, using abone-ligament-bone autograft. Cruciate ligament reconstruction has theadvantage of immediate stability and a potential for immediate vigorousrehabilitation. However, the disadvantages to ACL reconstruction aresignificant: for example, normal anatomy is disrupted when the patellartendon or hamstring tendons of the patient are used for thereconstruction; placement of intraarticular hardware is required forligament fixation; and anterior knee pain frequently occurs. Moreover,recent reviews of cruciate ligament reconstruction indicate an increasedrisk of degenerative arthritis with intraarticular ACL reconstruction inlarge groups of patients.

A second method of treating ACL injuries, referred to as “primaryrepair”, involves suturing the torn structure back into place. PrimaryACL repair has the potential advantages of a limited arthroscopicapproach, minimal disruption of normal anatomy, and an out-patientprocedure under a local anesthetic. The potential disadvantage ofprimary cruciate ligament repair is the perception that over the longterm, ACL repairs do not provide stability in a sufficient number ofpatients, and that subsequent reconstruction may be required at a laterdate. The success rate of such anterior cruciate ligament repair hasgenerally hovered in the 60% to 70% range.

The autogenous patellar tendon is an excellent tendon replacementsource, providing proper tendon length and bone blocks that are fullyosteointegrated without immunological rejection. Unfortunatelyharvesting autogenous bone-tendon-bone (hereinafter B-T-B) also has anumber of adverse effects, including donor morbidity (pain), patellarfracture, tendon rupture and degeneration of the patello femoralarticular surface. As an alternate to autogenous graft tissue, syntheticmaterials have previously received FDA approval. In this regardpolyester braids, steel wire and PTFE (GORE-TEX) have been usedsurgically. All of these materials have failed to integrate into thebone resulting in the tendon's inability to sustain the tensile andtorsional loads applied to the knee in normal usage. Nearly all of thesesynthetic repairs have been revised with autogenous and/or allografttissue.

There is a limited supply of allograft bone-patellar tendon- bone(B-PT-B) tissue due in large part to the number of donors that qualifyaccording to the selective donor acceptance criteria. As a result of thelimited number of available grafts there is a large demand for suchgrafts. Accordingly a cortical bone block geometry has been developed toprovide bone block fixation for an allograft or autograft tendon B-T-Bgraft with performance characteristics that meet or exceed conventionalB-T-B loads.

The use of substitute bone tissue dates back around 1800. Since thattime research efforts have been undertaken toward the use of materialswhich are close to bone in composition to facilitate integration of bonegrafts. Development have taken place in the use of grafts of a mineralnature such as corals, hydroxyapatites, ceramics or synthetic materialssuch as biodegradable polymer materials. Surgical implants should bedesigned to be biocompatible in order to successfully perform theirintended function. Biocompatibility may be defined as the characteristicof an implant acting in such a way as to allow its therapeutic functionto be manifested without secondary adverse affects such as toxicity,foreign body reaction or cellular disruption.

Human allograft tissue is widely used in orthopaedic, neuro-,maxillofacial, podiatric and dental surgery. The tissue is valuablebecause it is strong, biointegrates in time with the recipient patient'stissue and can be shaped either by the surgeon to fit the specificsurgical defect or shaped commercially in a manufacturing environment.Contrasted to most synthetic absorbable or nonabsorbable polymers ormetals, allograft tissue is biocompatible and integrates with the.surrounding tissues. Allograft bone occurs in two basic forms;cancellous and cortical. Cortical bone is a highly dense structurecomprised of triple helix strands of collagen fiber, reinforced withhydroxyapatite. The cortical bone is a compound structure and is theload bearing component of bones in the human body. The hydroxyapatitecomponent is responsible for the high compressive strength of the bonewhile the collagen fiber component contributes in part to torsional andtensile strength.

Many devices of varying shapes and forms can be fabricated fromallograft cortical tissue by machining. Surgical implants such as pins,rods, screws, anchors, plates, intervertebral spacers and the like havebeen made and used successfully in human surgery. These pre-engineeredshapes are used by the surgeon in surgery to restore defects in bone tothe bone's original anatomical shape.

Allograft bone is a logical substitute for autologous bone. It isreadily available and precludes the surgical complications and patientmorbidity associated with obtaining autologous bone as noted above.Allograft bone is essentially a collagen fiber reinforced hydroxyapatitematrix containing active bone morphogenic proteins (BMP) and can beprovided in a sterile form The demineralized form of allograft bone isnaturally both osteoinductive and osteoconductive. The demineralizedallograft bone tissue is fully incorporated in the patient's tissue by awell established biological mechanism. It has been used for many yearsin bone surgery to fill the osseous defects previously discussed.

The combination of natural cortical bone with very desirable mechanicalstrength and the addition of synthetic (recombinant) BMPs provides asuperior form of tissue for surgical use retaining all of the mechanicalproperties of the cortical component and the accelerated healing offeredby the BMPs.

U.S. Pat. No. 5,972,368 issued on Oct. 26, 1999 discloses the use ofcortical constructs (e.g. a cortical dowel for spinal fusion) which arecleaned to remove all of the cellular material, fat, free collagen andnon-collagenous protein leaving structural or bound collagen which isassociated with bone mineral to form the trabecular struts of bone. Itis stated that the natural crystalline structure of bone is maintainedwithout the risk of disease transmission or significant immunogenicity.Thus the shaped bone is processed to remove associated non-collagenousbone proteins while maintaining native bound collagen materials andnaturally associated bone minerals. The surface of a machined corticalbone surface is characterized by a wide variety of openings resultingfrom exposure by the machining process of the Haversian canals presentthroughout cortical bone. These canals serve to transport fluidsthroughout the bone to facilitate the biochemical processes occurringwithin the bone. They occur at variable angles and depths within thebone.

In French Patent Applications Nos. 2,582,517 and 2,582,518 treatment offragments of bones taken from animals, primarily cattle were partiallydemineralized and tanned with glutaraldehyde. The bone elements to beimplanted are cut to the desired shape from an ox bone which has beensubjected to a treatment comprising a degreasing step with an organicsolvent such as ethanol, a demineralization step with a calciumextraction agent such as hydrochloric acid and tanning withglutaraldehyde and subsequent washings. Similar demineralization of boneis shown in U.S. Pat. No. 5,585,116 issued Dec. 17, 1996. This patentalso notes that it is known that partial demineralization facilitatesintegration of a bone graft. This is accordingly followed by differentcomplementary steps which are intended either to deproteinize the bonecompletely or to act on the nature of the proteins which then remainlinked within the bone matrix or else to increase this proportion ofproteins.

Much of the structure and many of the properties of original tissues maybe retained in transplants through use of xenogeneic or heterograftmaterials, that is, tissue from a different species than the graftrecipient. For example, tendons or ligaments from cows or other animalsare covered with a synthetic mesh and transplanted into a heterologoushost in U.S. Pat. No. 4,400,833. Flat tissues such as pig pericardia arealso disclosed as being suitable for heterologous transplantation inU.S. Pat. No. 4,400,833. Bovine peritoneum fabricated into a biomaterialsuitable for prosthetic heart valves, vascular grafts, burn and otherwound dressings is disclosed in U.S. Pat. No. 4,755,593. Bovine, ovine,or porcine blood vessel heterografts are disclosed in WO 84/03036.However, none of these disclosures describe the use of a xenograft forACL replacement.

Xenograft materials must be chemically treated to reduce immunogenicityprior to implantation into a recipient. For example, glutaraldehyde isused to cross-link or “tan” xenograft tissue in order to reduce itsantigenicity, as described in detail in U.S. Pat. No. 4,755,593. Otheragents such as aliphatic and aromatic diamine compounds may provideadditional cross linking through the side chain carboxyl groups ofaspartic and glutamic acid residues of the collagen polypeptide.Glutaraldehyde and diamine tanning also increases the stability of thexenograft tissue.

U.S. Pat. No. 5,562,669 issued Oct. 8,1996 discloses a B-T-B. tendonanchor device using autologus bone plugs taken from the cores drilledout from the bone tunnels of the patient or alternatively donor bone,namely allograft bone to make the bone plugs. The linear cylindricalplug member is provided with two longitudinal substantially parallelgrooves cut on opposite sides of each bone plug which provide a recessin which the tendon can be seated. A notch may also be drilled ifdesired across one end of the bone plug so that the tendon can bewrapped alongside and around the end of the bone plug without protrudingexcessively from the plug. Suture holes can be cut through the bone plugfor attaching the tendon to the plug as is shown in FIGS. 4 a and 4 b.The perfectly symmetric pattern of the '669 presents the tendon equallyon both sides of the bone block.

Likewise U.S. Pat. No. 5,632,748 issued May 27, 1997 discloses a B-T-Btendon anchor device formed of plastic, bone, stainless steel or anyother suitable material. The body is tapered and formed with a groove toreceive a fixation screw and two curved recesses to hold a tendon whichis looped over the device. The fixation groove is provided with threads(FIG. 3) and the tendon grooves are provided with teeth. (FIG. 4). A twopiece version having a tongue and groove and stepped mating faces forjoinder with two tendon grooves is shown in FIG. 7.

U.S. Pat. No. 6,264,694 issued July 24, 2001 discloses a sphericalmember having a through going bore and parallel recessed surfaces whichenable it to be tied to the end of a soft tissue ligament graft to allowthe graft to be secured within the bone tunnel by an interference screw.

SUMMARY OF THE INVENTION

The present invention in various embodiments is directed to abone-tendon-bone composite graft for use in tendon and cruciate ligamentreconstruction. The process of the present invention is directed toligament or tendon reconstruction surgery. In the inventive surgicalinstallation, a bone tunnel is drilled in each of two bones of thejoint. In knee surgery, these are the femur and the tibia although otherjoints held in place by tendons could be substituted. The allograft boneblocks are pre-machined to form a cylindrical central through going boreand two longitudinal substantially parallel channels which are parallelto the axis of the central bore and are formed longitudinally along theouter surface of the bone block. A rounded recess is cut in the end ofthe bone block leading from the central bore to one of the channels. Atleast one tendon replacement member, such as a semitendinous, patellaror gracilis tendon or a combination of tendons is extended between thebone blocks through the central bore of each bone block and over an endconnector recess pathway and back along a parallel channel formed on theouter surface of each bone block. The tendon replacement is in turnattached to the two bone blocks. Each bone block is inserted into one ofthe bone tunnels and secured therein by an interference screw whichinserted into the other channel formed on the outside surface of thebone block. The use of the bone-tendon-bone composite graft of theinvention results in a reconstructed tendon.

The bone block for modular tendon assembly is directed toward a B-T-Bgraft for use in orthopedic surgical procedures. The substantiallycylindrical bone block invention is provided with parallel channels cutin the outer surface of the bone block to receive and hold a tendon andto accommodate a fixation screw. An end channel or guide way is cut intoa curved or tapered end of the bone block and leads from a channel intothe central bore to provide a pathway for the tendon loop. A radialthrough going suture bore is cut transversely to the axis of thechannels and at least a portion of the exterior surface of the blockopposite the screw fixation groove is provided with a plurality ofoutwardly extending teeth forming a toothed pattern or a radial ribpattern. The present invention overcomes the current problem of oversizing the outside diameter of the tendon-block construct which cannotbe overcome by making the tendon slot deeper so as to cause the tendonto ride deeper in the block. This slot deepening would weaken the boneblock by reduction of its effective cross-section so that the bone blockmight be crushed by the placement of the interference screw and thepressure created on the bone block.

It is thus an object of the invention to provide a shaped bone implantconstruct having a fully mineralized bone block or a partiallydemineralized cortical bone layer with an interior mineralized bonesection to provide compression strength to the implant bone construct.

It is another object of the invention to utilize a partiallydemineralized shaped bone implant structure to approximate themechanical strength characteristics of a natural bone-tendon-bone toprovide overall strength and initial durability to the structure.

It is also an object of the invention to provide a pre-machined bonederived structure which can effectively promote new bone growth andaccelerate healing.

It is an additional object of the invention to construct a bone block ofthe inventive design to provide a significantly thinner bone blockcross-sectional diameter.

It is yet another object of the invention to create a bone-tendon-boneassembly which mimics the asymmetrical configuration of naturalbone-tendon-bone constructs.

It is also an object of the invention to create a bone-tendon-boneassembly which can be easily handled by the physician during surgerywhich eliminates or significantly reduces the physician from carving therespective bone blocks.

These and other objects, advantages, and novel features of the presentinvention will become apparent when considered with the teachingscontained in the detailed disclosure which along with the accompanyingdrawings constitute a part of this specification and illustrateembodiments of the invention which together with the description serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a standard prior art bone-tendon-boneimplant;

FIG. 2 is a perspective view showing tunnel preparation for theinventive bone-tendon-bone assembly;

FIG. 3 is a view of the knee showing the tibia and femur with tunnelscut there through;

FIG. 4 is a perspective view of the inventive bone-tendon-bone assemblyimplanted and secured in a knee joint;

FIG. 5 is an enlarged perspective view of the inventive bone-tendon-boneassembly of FIG. 4 prior to implantation in a knee Joint;

FIG. 6 is a perspective view of the inventive bone block;

FIG. 7 is a perspective view of the bone block of FIG. 6 in a reverseand rotated orientation;

FIG. 8 is an end view of the bone block of FIG. 7 taken from end view8′-8′;

FIG. 9 is a perspective view of another embodiment of the inventive boneblock with an exterior thread;

FIG. 10 is a perspective view of the bone block of FIG. 9 in a rotatedorientation;

FIG. 11 is an end view of the bone block of FIG. 10;

FIG. 12 is an enlarged partial view of a rib section of FIG. 9 takenfrom section 12′- 12′;

FIG. 13 is a perspective view of an alternate embodiment of theinventive bone block having an oval cross section;

FIG. 14 is a perspective view of the bone block embodiment of FIG. 13 ina reverse and rotated orientation;

FIG. 15 is an end view of the bone block embodiment of FIG. 13;

FIG. 16 is a perspective view of the alternate embodiment of theinventive bone block with an exterior thread;

FIG. 17 is a perspective view of the bone block embodiment of FIG. 16 ina reverse and rotated orientation; and

FIG. 18 is an end view of the bone block embodiment of FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiment and best mode of the present invention is shownin FIGS. 4-8.

As shown in the drawings, a reconstructed bone-tendon-bone (B-T-B)assembly 10 for a knee joint is shown in FIG. 4 in accordance with thepresent invention. The cruciate ligament reconstruction surgicaloperation can be conducted as an open orthopedic surgery, or througharthroscopic surgery. While the description of the invention is praril ydirected to knee reconstruction, the present invention can easily beadapted to other joints requiring ligament or tendon replacement.

A number of surgical methods and variation of the same can be used inthe knee tendon reconstructive surgery. Representative methods which areexemplary but not exclusive or limited are referred to as the Lipscom etal. Technique, the Puddu Technique, the Zaricznyj Technique, the Zarinsand Rower Techniques and are set forth and fully explained in Chapter29, Knee Injuries, Campell's Orthopaedics (1998, 9^(th) Ed.) and areincorporated herein by reference. In most B-T-B procedures anteromedialand distal lateral bores are drilled to give access to the knee jointfor these procedures.

In the standard ACL reconstruction, the intercondylar notch is preparedby drilling the femoral tunnel of the ACL. The tibial hole is preparedby drilling using a cannulated reamer of 8 mm to 12 mm diameter and theintra-articular fluid is drained. The cannulated system is used to placethe tunnels anatomically over a guide wire in the tibial and femoralanatomy. The tibial tunnel entrance is midway between the tibialtubercle and the posterior medial edge of the proximal tibia,approximately 3 finger breadths below the joint line. The exit for thetibia tunnel is the posterior medial footprint of the native ACL. Withethe knee positioned at 90 degrees of flexion, the guide pin is placed inthe intercondylar notch and exits the superior lateral femur just abovethe flare of the condyle. The femoral tunnel is then placed using acannulated reamer over the guide wire to accommodate a bone block. Thegraft is passed into position in the femoral tunnel and fixed with aninterference screw.

The two major bones that meet at the knee joint are the tibia 22 and thefemur 24. Bone tunnels 23 and 25 are drilled through each of these twobones 22,24 respectively. The tunnels 23 and 25 may be drilled with aregular drill that crushes and removes the bone within the tunnel but itis preferable to use a coring reamer to drill the bone tunnels. Thereamer drills out a core of bone through each of the bone tunnels. Theknee is flexed or extended a variable amount in order to properlyposition the femoral tunnel. The reamer is then directed through thetibial tunnel for drilling in and through the femur. The bone core fromthe femur is removed. Standard deburing and debridement procedures arefollowed.

After the cores have been drilled out forming the bone tunnels 23 and25, an allograft B-T-B assembly with pre-machined bone blocks 30 and anattached treated tendon member(s) 50 is inserted into the bone tunnelsby pulling the respective bone blocks into the tunnels via sutures 26 asseen in FIG. 4 with the bone blocks being fixed in the tunnel by aninterference screw 28 which engages the bone block and the tibia and/orfemur to hold the tendon in place. The tendon(s) pass through a blockcentral bore and along an external channel. As can be seen in FIGS. 4-8a bone block body 30 is cut into a cylindrical shape typically rangingfrom 8 mm to 12 mm in diameter with a curved outer surface 31 and has acentral through going bore 32 cut there through along the anatomicalcanal and two longitudinal substantially parallel channels 34 and 36 cutinto the outer surface 31 of the bone bock to provide a surface forseating the looped tendon 50 and inserting an interference fixationscrew 28 to hold the bone block 30 in place in the tunnel. Channels 34and 36 are preferably cut in the exterior surface of the block so thatthe midpoint axis of each channel falls at a 45 degree angle taken froma diameter line running through a mid point of the arc between thechannels. Thus both channels fall on the same semi-circle of thecylindrical bone block. The bone block diameter can vary from 8-12 mmwith a corresponding length of 25-35 mm depending upon surgeonpreference. An end recess or pathway 33 is cut into the end of the boneblock body 30 forming a recessed pathway leading to the central bore 32and parallel channel 34 so that the tendon(s) 50 can be looped over acurved surface so that there will be no sharp edges engaging thetendon(s) 50 as is shown in FIG. 5. Suture holes 37 are radially cutthrough the bone block from the channel 34 into the central bore 32 forattaching the tendon(s) 50 to the bone block 30. The suture holes aredrilled into the channel 34 radially through the bone block. In thepreferred embodiment, at least two (2) such suture holes 37 are drilledthrough the bone block. The sutures 26 are used to pull the bone blockinto the desired location in tunnels 23 and 25 and the pre-drilledsuture holes in the bone face are located at the bone face at a locationso as not to have the suture 26 cut by the interference screw 28. Aplurality of circulation holes 38 are cut radially into the surface ofthe bone block body leading from the outer surface 31 to the centralcore 32 to expose the interior of the bone block and allow faster bonegrowth. These holes preferably have a diameter of 1 mm or less. Aplurality of angularly shaped teeth 39 are cut into the outer surface 31in parallel rows equidistantly spaced apart to provide additionalgripping of the bone block 30 in the tunnel. The teeth 39 are preferablyformed or cut with a vertical face 40 and a sloping angled face 41 cutat a 40 degree angle as is shown in FIG. 6. It is of course within thescope of the invention to stagger the rows of teeth to present multiplevariations of same or to apply a thread or ridge on the outside exteriorsurface. The teeth 39 are located on only one side the bone block body30 as can be readily seen in FIG. 7. The inner end face 42 of each boneblock is cut on an angle or beveled to provide a flush alignment of thebone block with the articulating end of the tunnel at both the tibialand femoral placement. This will minimize the contact between the boneblock and the articulating cartilage on the faces of the knee joint. Thefemoral angle will preferably have a range from 5 to 15 degrees andtibial angle from 15 to 30 degrees.

As can be seen in the rib variation of FIGS. 9-12, the teeth 39 havebeen replaced with a rib structure. A plurality of ribs 44 are cut intothe outer surface 31 equidistantly spaced apart to provide additionalgripping of the bone block 30 in the tunnel. The ribs 44 are cut withtwo 45 degree angled sides 45. While only suture holes 37 are shown,circulation holes can also be cut from the surface to the central bore.

As can be seen in FIGS. 13-15 in an alternate embodiment, a bone blockbody 130 is cut into a longitudinal form with an oval or ellipticalcross sectional shape typically ranging from 8 mm to 12 mm in the majordiameter axis with a curved outer surface 131 and has a central throughgoing bore 132 cut there through. Two longitudinal substantiallyparallel channels 134 and 136 are cut into the outer surface 131 of thebone bock to provide a surface for seating the looped tendon(s) 50 andinserting an interference fixation screw 28 to hold the bone block 130in place in the tunnel. Channels 134 and 136 are preferably cut in theexterior surface of the block 130 so that the midpoint axis of eachchannel falls at a 45 degree angle taken from a diameter line runningthrough a mid point of an arc between the channels. Thus both channelsfall on the same side of the bone block. The bone block can vary from8-12 mm at its major diameter with a corresponding length of 25-35 mmdepending upon surgeon preference. An end guide path or pathway 133 iscut into the end of the bone block body 130 forming a recessed pathwayleading to the central bore 132 and parallel channel 134 with thetendon(s) 50 being looped over a curved surface so that there will be nosharp edges engaging the tendon(s) 50. Suture holes 137 are radially cutthrough the bone block from the channel 134 into the central bore 132for attaching the tendon(s) 50 to the bone block 130. The suture holesare drilled into the channel 134 radially through the bone block. In thepreferred embodiment, at least two (2) such suture holes 137 are drilledthrough the bone block. Sutures 26 are used to pull the bone block 130into the desired location in tunnels 23 and 25 and the pre-drilledsuture holes in the bone face are located at the bone face at a locationso as not to have the suture 26 cut by the interference screw 28. Aplurality of circulation holes 138 are cut radially into the surface ofthe bone block body leading from the outer surface 131 to the centralcore 132 to expose the interior of the bone block bone and allow fasterbone growth. A plurality of shaped teeth 139 are cut into the outersurface 131 in parallel rows equidistantly spaced apart to provideadditional gripping of the bone block 130 in the tunnel. The teeth 139are preferably formed or cut with a vertical face 140 and a slopingangled face 141 cut at a 40 degree angle. It is of course within thescope of the invention to stagger the rows of teeth to present multiplevariations of same or to apply a thread or ridge on the outside exteriorsurface. The teeth 139 are located on only one side the bone block body130 as can be readily seen in FIG. 13 with the other side presenting asmooth surface 135. The inner end face 142 of each bone block is cut onan angle or bevel to provide a flush alignment of the bone block withthe articulating end of the tunnel at both the tibial and femoralplacement. This will minimize the contact between the bone block and thearticulating cartilage on the faces of the knee joint. The femoral anglewill preferably have a range from 5 to 15 degrees and tibial angle from15 to 30 degrees.

As can be seen in FIGS. 16-18 the teeth 139 have been replaced with arib structure. A plurality of ribs 144 are cut into the outer surface131 equidistantly spaced apart to provide additional gripping of thebone block 130 in the tunnel. The ribs 144 are cut with two 45 degreeangled sides.

The asymmetry of the inventive design also provides a significantlythinner bone block cross-sectional diameter, This is critical during theentry and proper placing of the bone block in the tunned drilled by thesurgeon. Thus the tendon is placed in an asymmetric orientation relativeto the bone block. This is very much like the symmetry in the patellarbone-tendon-bone (either autologous or allogenic). The success of thepatellar BTB in providing satisfactory load bearing and eventual healingin the ACL application may be in part due to the asymmetry.

When using multiple strands of tendons 50, as an example, asemitendinosus tendon and/or gracilis tendon are extended between bothof the bone blocks 30, 130. The tendon(s) 50 are preferably sutured tothemselves to form a double loop as shown in FIGS. 4 and 5. Sutures 26are also used through the suture holes 137 to attach the tendon(s) toeach of the bone blocks. The ligament replacement of an embodiment ofthe invention may include one or more of the following tendons:patellar, semitendinosus, gracilis, quadriceps, adductor magnus, thehamstrings, peroneus longus and hallucis longus. The tendons typicallyrun from 180 mm to 200 mm in length and when harvested are fresh frozenor freeze dried after cleaning for preservation for use in the B-T-Bassembly. The tendon can be sterilized with radiation dosages as is wellknown in the art. As such the tendon structure or member combining oneor more of the above noted tendons will connect the two bone blocks.Single bone blocks can be used with the achilles, biceps femoris andquadriceps tendons as these come naturally with a bone block.

Still further embodiments of the invention may substitute or combine manmade or artificial fibers or human tissue for the tendons for use as theligament replacement. After the bone blocks have been inserted in thebone tunnels, the sutures 26 hanging from one end of the composite graftare attached to a needle, a passer or other conventional graft placementtool.

The proper tension is then applied to the graft by pulling on the suture26 hanging out from the tibial incision. A driver and a headlessinterference screw are then inserted through the tibial incision fordriving the screw along the channel 36, 136 of the bone block. Inaffixing the composite graft 10 within a bone tunnel, contact between aninterference screw 28 and the tendon 50 should be avoided so as not tocut or tear the tendon. To better insure that the screw is out ofcontact with the tendon, the interference screw 28 should be drivenalong the bone portion of the bone block channel 36, 136 and therespective bone tunnel wall. The sutures 26 are then cut and theincisions are closed.

While this operation has been discussed in terms of using allograft boneblocks, alternative sources of bone blocks may be substituted such asxenograft bone or synthetic graft materials. With any of thesealternatives, the bone blocks may be shaped as described above for thegraft.

The unique features of bone that make it desirable as a surgicalmaterial are, its ability to slowly resorb and be integrated into thespace it occupies while allowing the bodies own healing mechanism torestore the repairing bone to its natural shape and function by amechanism known in the art as creeping substitution. The second featureis the high mechanical strength arising from the collagen fiberreinforced hydroxyapatite compound structure. The creeping substitutionmechanism, takes considerable time and some forms of cortical bone intheir natural, unmodified biological state have been found to persistfor over one year before completely remodeling. Thus a means ofaccelerating the rate of biointegration of cortical bone would improvethe rate of healing and benefit the recipient patient.

The cylindrical cortical bone block 30, 130 can have its surface 31, 131and or central cavity 32, 132 modified by acid treatment to remove alayer of the inorganic mineral. Thus the surface of cortical boneconstructs can be modified by acid treatment to remove a layer of theinorganic, mineral material in such a way as to leave the mechanicalproperties substantially unchanged or to provide a construct havingsuitable compression and bending strength. This allows the addition ofBMP's and other desirable additives which are more fully set forth onpages 15 and 16 to be introduced to the surface and thereby enhance thehealing rate of the cortical bone in surgical procedures. The processalso exposes the naturally occurring BMP's near the surface and rendersthe surface with biological properties similar to fully demineralizedbone (DMB). The inner mass of the bone construct would be left intact tocontain the naturally occurring BMP's.

It is well known that bone contains osteoinductive elements known asbone morphogenetic proteins (BMP). These BMP's are present within thecompound structure of cortical bone and are present at a very lowconcentrations, e.g. 0.003%. BMP directs the differentiation ofpluripotential mesenchymal cells into osteoprogenitor cells which formosteoblasts. The ability of freeze dried demineralized cortical bone tofacilitate this bone induction principle using BMP present in the boneis well known in the art. However, the amount of BMP varies in the bonedepending on the age of the bone donor and the bone processing. Basedupon the work of Marshall Urist as shown in U.S. Pat. No. 4,294,753,issued Oct. 13, 1981 the proper demineralization of cortical bone willexpose the BMP and present these osteoinductive factors to the surfaceof the demineralized material rendering it significantly moreosteoinductive. The removal of the bone mineral leaves exposed portionsof collagen fibers allowing the addition of BMP's and other desirableadditives to be introduced to the demineralized outer treated surface ofthe bone structure and thereby enhances the healing rate of the corticalbone in surgical procedures. The treatment process also exposes thenaturally occurring BMP's at the surface and renders the surface withbiological properties similar to full demineralized bone (DBM). Theinner mass of the bone mineral of the shaped bone block construct wouldbe left intact to contain the naturally occurring BMP's and traceelements as noted above.

The bone blocks of the present invention were prepared by machiningfibula although femoral, femoral or tibia cortical bone and bone takenfrom the humerus, ulna or radius can be used.

It is also possible to add one or more rhBMP's to the surface of thetreated bone shape by soaking and being able to use a significantlylower concentration of the rare and expensive recombinant human BMP toachieve the same acceleration of biointegration. The addition of otheruseful treatment agents such as vitamins, hormones, antibiotics,antiviral and other therapeutic agents could also be added to thesurface modified layer.

Any number of medically useful substances can be incorporated in thebone block and tendon assembly by adding the substances to the assembly.Such substances include collagen and insoluble collagen derivatives,hydroxyapatite and soluble solids and/or liquids dissolved therein. Alsoincluded are antiviricides such as those effective against HIV andhepatitis; antimicrobial and/or antibiotics such as erythromycin,bacitracin, neomycin, penicillin, polymyxin B, tetracycline, viomycin,chloromycetin and streptomycin, cefazolin, ampicillin, azactam,tobramycin, clindamycin, gentamycin and silver salts. It is alsoenvisioned that amino acids, peptides, vitamins, co-factors for proteinsynthesis; hormones; endocrine tissue or tissue fragments; synthesizers;enzymes such as collagenase, peptidases, oxidases; polymer cellplscaffolds with parenchymal cells; angiogenic drugs and polymericcarriers containing such drugs; collagen lattices; biocompatible surfaceactive agents, antigenic agents; cytoskeletal agents; cartilagefragments, living cells such as chondrocytes, bone marrow cells,mesenchymal stem cells, natural extracts, tissue transplants,bioadhesives, transforming growth factor (TGF-beta), insulin-like growthfactor (IGF-1), platelet derived growth factor, fibroblast GF,osteopontin VEGF, blood elements; growth hormones such as somatotropin;bone digestors; antitumor agents; fibronectin; cellular attractants andattachment agents; Immuno-suppressants; permeation enhancers, e.g. fattyacid esters such as laureate, myristate and stearate monoesters ofpolyethylene glycol, enamine derivatives, alpha-keto aldehydes can beadded to the composition.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.However, the invention should not be construed as limited to theparticular embodiments which have been described above. Instead, theembodiments described here should be regarded as illustrative ratherthan restrictive. Variations and changes may be made by others withoutdeparting from the scope of the present invention as defined by thefollowing claims:

1. A sterile composite graft comprising: first and second bone blocks,each bone block defining a central through going bore having a crosssection which will allow a ligament replacement assembly to be passedthere through and at least one longitudinal channel cut substantiallyparallel to the axis of the central through going bore in the exteriorsurface of said bone block and a ligament replacement mounted to saidbone blocks, said ligament replacement assembly extending through saidcentral bore of said bone blocks and around said first and second boneblocks seated in said longitudinal channel, said ligament replacementassembly comprising a plurality of tendons taken from a group of tendonsconsisting of a semitendinous tendon, a patellar tendon, gracilistendon, quadriceps tendon, adductor magnus tendon, peroneus tendons,tibialis tendons and hallucis achilles tendon.
 2. (canceled)
 3. Asterile composite graft as claimed in claim 1 wherein said first andsecond bone blocks are cylindrical in shape and further include at leastone suture hole drilled radially through each of said bone blocks fromone of the longitudinal channels through to the central bore.
 4. Asterile composite graft as claimed in claim 1 wherein said first andsecond bone blocks further define a rounded notch in one end leadingfrom said central bore to a parallel longitudinal channel to accommodatesaid ligament replacement assembly extending around said bone block fromsaid central bore to a parallel longitudinal channel.
 5. A sterilecomposite graft as claimed in claim 1 wherein said first and second boneblocks further comprise a plurality of holes drilled radially througheach of said bone blocks from an outer surface through to the centralbore.
 6. A sterile composite graft as claimed in claim 1 wherein saidfirst and second bone blocks are constructed of allograft cortical bone.7. A sterile composite graft as claimed in claim 1 wherein said firstand second bone blocks are constructed of xenograft cortical bone.
 8. Asterile composite graft as claimed in claim 1 wherein said first andsecond bone blocks are constructed of ceramic.
 9. A sterile compositegraft as claimed in claim 1 wherein said first and second bone blocksare constructed of bioabsorbable polymers.
 10. (canceled)
 11. (canceled)12. A sterile composite graft as claimed in claim 1 wherein said firstand second bone blocks have a second fixation screw channel cut in theirouter surface.
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 29. (canceled)30. A sterile bone-tendon-bone assembly comprising: first and secondcylindrical allograft bone blocks defining a central bore and at leastone longitudinally running channel formed on the exterior surface ofsaid bone block; a first tendon replacement strand extending betweensaid first and second bone blocks through said central bore andlongitudinally alongside each of said first and second bone blocks; anda second tendon replacement strand extending between said first andsecond bone blocks through said central bore and longitudinally alongthe sides of each of said first and second bone blocks adjacent to atleast a portion of said first tendon replacement strand.
 31. The sterilebone-tendon-bone assembly of claim 30 wherein said first and second boneblocks each have at least one suture hole extending radially throughsaid bone block from said central bore through to said substantiallyparallel channel with a suture extending through said at least onesuture hole radially cut in each of said bone blocks leading into saidcentral bore to attach said ligament replacement strands to said firstand second bone blocks.
 32. The sterile bone-tendon-bone assembly ofclaim 30 wherein said at least one of said tendon replacement strands isxenograft tissue.
 33. The sterile bone-tendon-bone assembly of claim 30wherein said at least one of said tendon replacement strands isallograft tissue
 34. (canceled)
 35. A sterile composite graft as claimedclaim 30 wherein each bone block includes an additive taken from a groupof additives consisting of living cells such as chondrocytes, bonemarrow cells, mesenchymal stem cells, natural extracts, tissuetransplants, bioadhesives, transforming growth factor (TGF-beta),insulin-like growth factor (IGF-1), platelet derived growth factor,fibroblast GF, osteopontin VEGF, blood elements.
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